The present invention relates to polyols, urethane polymers comprising the polyols and reactive hot melt adhesive compositions comprising the urethane polymers and the process of making the polyols, urethane polymers and reactive hot melt adhesive compositions.
In conventional hot melt adhesives, typically a polymer, a tackifier, and a selection of other additives such as antioxidants, are mixed together to produce an adhesive composition. These materials tend to form bonds through their rapid solidification from the melt. These materials have the advantage of being relatively easy to apply. However hot melt adhesives are typically not reactive in nature and therefore do not develop sufficient strength and sufficient heat and chemical resistance for certain applications.
In order to impart sufficient structural, heat and chemical resistance to adhesive formulations, reactive or curable compositions are conventionally used. These materials tend to form durable bonds through a chemical reaction and as such are the adhesives of choice for various applications and substrates. However, reactive or curable compositions are typically lacking in versatility on the combined property characteristics of xe2x80x9cgreenxe2x80x9d strength and xe2x80x9copenxe2x80x9d time. This lack of process versatility makes the compositions handling characteristics poor and limits the composition""s utility in some assembly operations.
In polyurethane reactive hot melt adhesives (polyurethane Rhma), an isocyanate terminated urethane polymer is produced through the polymerization of polyols and excess polyisocyanate compounds.
Polyurethane Rhma(s) typically are cured in the presence of moisture. Moisture, which is present in the ambient atmosphere, reacts with the isocyanate end groups to cause chain extension and or crosslinking. As a result of this curing reaction, polyurethane Rhma develop temperature and chemical resistance. A typical cured polyurethane Rhma would generally exhibit a degree of stiffness as well as toughness. Toughness of polyurethane Rhma is attributed to long chain polyols called xe2x80x9csoft segmentsxe2x80x9d. Stiffness of the polyurethane Rhma is attributed to relatively short chain, high Tg, regions called xe2x80x9chard segmentsxe2x80x9d.
Typically, polyurethane Rhma(s) do not exhibit sufficient combined green strength and open time for many manufacturing processes. Also, while moisture cured polyurethane Rhma exhibit good temperature resistance when compared to typical hot melt adhesives, a need exists for a polyurethane Rhma that exhibit a desirable balance of processing, thermal and mechanical attributes.
Those skilled in the art of formulating polyurethane Rhma(s) have used so-called xe2x80x9cmodifiersxe2x80x9d in an attempt to improve the balance of processing, thermal and mechanical attributes of polyurethane Rhma(s). These conventional modifiers have included rosin glycerol ester, polycaprolactone diol and terpene phenolic resins. These modifiers have not provided a viable solution to the formulators"" needs and hence a need still exists for a modifier that can provide a useful balance of processing, thermal and mechanical attributes to polyurethane Rhma(s).
The present invention relates to new polyols, urethane polymers made from these polyols and reactive hot melt adhesive compositions which include the urethane polymers.
The present invention particularly relates to polyols comprising the reaction products of a polyesterification process employing monocarboxylic acids, polyhydric alcohols and dicarboxylic acids as reactants. The polyol of the present invention has a glass transition temperature (Tg) in the range of aboutxe2x88x9220xc2x0 C. to about +45xc2x0 C. as determined by Differential Scanning Calorimeter (DSC). Additionally, the polyol has a hydroxyl functionality ranging from 0.1 to 4.
The polyols of this invention have utility in polyurethane compositions and confer upon such compositions a desirable balance of processing, mechanical and thermal attributes, particularly when such compositions are used as reactive hot melt adhesives.